/* Selectors and properties */
body {
  font-family: 'Arial', sans-serif;
  background-color: #f0f0f0;
  margin: 0;
  padding: 0;
}

header {
  background-color: #333;
  color: white;
  padding: 10px;
  text-align: center;
}

section {
  margin: 20px;
}

h1 {
  color: #333;
}

p {
  line-height: 1.5;
}

/* Class and ID selectors */
.container {
  width: 80%;
  margin: 0 auto;
}

#main-content {
  background-color: #fff;
  padding: 15px;
  border-radius: 5px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

/* Media queries for responsive design */
@media screen and (max-width: 600px) {
  body {
    font-size: 14px;
  }
}